Researchers say Mount Aso discharged around 510,000 tons of ash and volcanic rock when it erupted on Saturday.
The figure is more than 10 times that of an eruption in September of last year and is on a par with the eruption of 1979.
Researchers at Kumamoto University and other parties calculated the amount of debris by collecting samples and conducting an aerial survey of the volcano in Kumamoto Prefecture.
The team found volcanic rocks measuring 5 to 10 meters in diameter near the No.1 crater of the Nakadake peak, where the explosive eruption occurred.
They also found a layer of accumulated debris in the area a meter to a meter and a half thick.
The team says ash and smaller stones were found more than 2 kilometers from the crater.
Associate Professor Yasuo Miyabuchi of Kumamoto University says that, since the current calculation does not include ash carried to far-away regions, the total amount could be more.
Source: NHK Image: ANN
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